Eco-friendly materials like carbohydrate-based polymers are important for a sustainable future. Starch is particularly promising because of its biodegradability and abundance but its processing to thermoplastic starch requires optimization. Here we developed thermoplastic maize starch materials based on three manufacturing protocols, namely: (1) starch/glycerol manual mixing and extrusion, (2) starch/glycerol manual mixing, extrusion, and kneading, (3) starch/glycerol/water manual mixing and kneading. The physical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and broadband dielectric spectroscopy. As expected from a partially miscible blend, the dielectric spectra revealed two distinct α-relaxations for the glycerol-rich and the starch-rich phases, respectively. By employing kneading after extrusion, the miscibility between the two phases was found to improve based on thermal and dielectric methods. Moreover, the addition of water during the premixing stage was observed to facilitate phase separation between starch and glycerol, with the α-relaxation dynamics of the latter being comparable to pure glycerol.

Carbohydrate polymers are promising materials for an eco-friendly future due to their biodegradability and abundance in nature. However, due to their molecular characteristics and hydrophilicity, are often complicated to be investigated via spectroscopic methods. Thermoplastic starch plasticized by glycerol was prepared through melt processing conditions using twin screw extruder. Here we show how the presence of water molecules affects the dielectric response and charge transport dynamics over broad frequency (10⁻¹ to 10⁷ Hz) and temperature (− 140 to 150 ^oC) ranges. Overall, 7 dielectric processes were observed and differentiation between electronic and ionic conductivities was achieved. Two segmental relaxation processes were observed for each sample, ascribed to the starch-rich and glycerol-rich phases. Although the timescales of the two segmental relaxations were found different, both arise from the same temperature, giving thus an alternative explanation on what is reported in the literature. The origin of the σ-relaxation was attributed to hydrogen ions and was found to be proportional to the ionic conductivity according to the Barton, Nakajima and Namikawa relation. The presence of water molecules was found to enhance the ionic conductivity, indicating that water contributes charge carriers when compared to the dried sample. Graphical Abstract: [Figure not available: see fulltext.]